Electrical actuator having a direct current motor

ABSTRACT

An electrical mains-powered actuator designed to operate a closing, darkening or solar protection element, having in a common enclosure, a direct current motor, a board controlling the motor power supply and an AC/DC voltage converter, the control board including a radio-wave receiver, such that the voltage converter enables lowering of the voltage and includes at least one switch controlled at a frequency (F 1 ) such that it is at most equal to twice the mains sector frequency or such that its ratio to the radio-wave receiver frequency (F 0 ) ranges between 2.2 10 −5  to 2.2 10 −4 .

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a 371 national phase application of PC1/IB03/04292 filled Sep.9, 2003, claiming priority to French Patent Application No. 0212618filed Oct. 10, 2002, the contents of which are incorporated herein byreference.

FIELD OF THE INVENTION

The invention relates to an electrical mains-powered actuator designedto operate a closing, darkening or solar protection element.

BACKGROUND

These actuators are often contained in a cylindrical enclosure when theycontrol the movement of roller blinds and in a parallelepipedalenclosure when they control the movement of venetian blinds.

Apart from very specific applications requiring an independentaccumulator battery and/or solar panel type power supply, theseactuators are powered from the low voltage (LV) AC mains supply(electric power grid, 110 to 230 V, 50 or 60 Hz, depending on countries)and the electric motors used in these actuators are normally ofsingle-phase asynchronous type (induction motor) with permanentcapacitor.

However, it is proving advantageous to replace such alternating currentmotors with permanent magnet DC motors, designed to operate at an extralow voltage (ELV), that is, more often than not, less than 48 V. Suchmotors are produced in very large quantities, in particular forautomobile applications, and their cost is therefore low.

Furthermore, the DC motor is well known to offer wide flexibility ofuse. In practice, the rotation speed can be controlled by the rotorpower supply voltage and obstacles can be detected by analyzing therotor current which reflects the motor torque.

However, converting a low voltage AC electrical source into an extra lowvoltage DC source raises problems. Indeed, the dimensions of thecomponents required lead to a physical separation between the powersupply converter and the actuator. This separation is not practical: itmeans having to arrange a second location to accommodate the powersupply module and, above all, having to provide a large section cableconnecting line to power the DC motor. This connecting line alsopresents the drawback of radiating interference generated by theelectrical switching action of the motor commutator.

Patent FR 2 692 418 discloses a solution to this type of problem. Itproposes, like other documents of the state of the art, that eachvenetian blind casing should simultaneously house the extra low voltageDC motor, a battery and a converter device formed by a transformer and arectifier (FIG. 3 of this patent). The battery is used to store energy.Because of this, the converter device is simply dimensioned for slowrecharging of the battery, which means that its dimensions can bereduced. There is nothing in this embodiment to suggest grouping all ofthese elements in the actuator: they are clearly represented physicallyseparate within the casing. However, for issues of battery life andmaintenance, it makes sense to allow for its easy replacement.

Such a solution presents an obvious drawback: it limits the number ofoperations to the battery capacity, which can be recharged only slowly.

Patent application EP 0 852 281 discloses a tubular actuator comprisinga reduction gear, a DC motor and an electronic control board alsoserving as mains powered power supply. It states that this board can ineffect be used to replace the transformer, the size of which isincompatible with installation in the tube. The solution recommended inthis document consists in replacing such elements with a powerelectronic unit comprising a coil mounted on a ferrite core, a diode, arectifier bridge and a capacitor.

It also states that the remote control of the actuator can be achievedby known means such as an infra-red link or a radio-wave link.

The problem raised by this arrangement lies in the miniaturizationconstraints evoked in the prior art, but also in the cohabitationrelationships between the various elements. In practice, the latterdissipate and receive thermal energy, although their own performancecharacteristics are affected by temperature, send and receiveelectromagnetic interference, although the performance of one of them isdirectly affected by the electromagnetic field and, finally, send andreceive conducted interference on their power supply line.

Patent application EP 1 091 078 discloses a motorized blind device inwhich the motor is of low voltage type and is powered from the mainssupply via a low voltage AC/DC converter. The use of a low voltage motorraises certain problems. In practice, these motors are difficult toproduce and are expensive. In the proposed embodiment, the operation ofthe converter runs the risk of disturbing the command receiver locatednearby.

Also, in a quite different field, patent U.S. Pat. No. 5,818,703discloses a voltage step-up DC/DC converter intended to power a cardiacdefibrillator, the switch of which operates at high frequency.

The object of the invention is to improve the actuators of the prior artand resolve the abovementioned problems. In particular, the inventionproposes to combine within a given space, a DC motor, a motor powersupply control board and a voltage converter, the control boardcomprising a radio-wave receiver. The operation of such an actuator mustalso be reliable.

SUMMARY OF THE INVENTION

The electrical mains-powered actuator is designed to operate a closing,darkening or solar protection element. It includes, in a commonenclosure, a direct current motor, a board controlling the motor powersupply and an AC/DC voltage converter. The control board includes aradio-wave receiver. The voltage converter enables lowering of thevoltage and includes at least one switch controlled at a frequency suchthat it is at most equal to twice the mains sector frequency or suchthat its ratio to the radio-wave receiver frequency ranges between 2.210⁻⁵ to 2.2 10⁻⁴.

Starting from the prior art requiring no electrical energy storagebattery, it has been observed in the context of the work leading to thepresent invention that miniaturizing a converter having sufficient powerto simultaneously power a radio-wave receiver, logical control elementsand, primarily, the DC electric motor, requires the presence of at leastone controlled switch, with a predefined frequency, this element beingessential for obtaining satisfactory thermal performance. The fact ofusing a controlled switch also means that a small-sized transformer canbe used. For given space constraints and for an actuator provided with aradio-wave receiver, it has also been observed that there is a trade-offin the choice of the control frequency of the switch to minimize theoverall cost of the solution.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended drawing represents, by way of example, an embodiment of theactuator according to the invention.

FIG. 1 is a diagrammatic view of an actuator according to the invention;and

FIG. 2 is a graph representing, on the y axis, the costs of producingthe actuator according to the invention according to the ratio of thecontrol frequency of the switch in the converter and, on the x axis, theoperating frequency of the radio-wave receiver.

In representative power and space conditions, the radio-wavetransmission frequency should be greater than 4500 times the controlfrequency of the switch.

The choice of a switch control frequency equal to twice the frequency ofthe mains supply, and synchronized on the latter, provides for the bestperformance/cost trade-off.

Such a choice is compatible with the use of a conventional transformer,with plates and no ferrite core, this transformer being significantlysmaller than that which would be required in the case of a conventionalpower supply provided with a transformer and a rectifier.

DETAILED DESCRIPTION

An actuator 10 represented in FIG. 1 takes from the AC electrical mainssupply a power P1 to convert it into mechanical power P2 on an outputshaft. The mechanical power P2 output is substantially lower than theelectrical power P1 drawn at the input, because of losses within theactuator.

A step-down AC/DC converter 3, or power supply unit (referred tointerchangeably herein) provides the required conversion from an AC lowvoltage into a DC extra low voltage. Naturally, its output voltage neednot necessarily be strictly constant and major fluctuations associatedwith the frequency of the mains supply may even be accepted (forexample, a ripple factor of 10 to 30%). For motor noise issues, there isnevertheless an interest in reducing this ripple.

This voltage is transmitted to an extra low voltage DC motor 5 via acontrol board 4 comprising in particular a radio-wave receiver 41. As inthe above-mentioned prior art, the radio-wave receiver receives thecontrol signals sent by a remote control, not represented but widelyknown to those skilled in the art. The receiver 41 is tuned to operateat a frequency denoted F0. Its antenna can be external or internal tothe enclosure 7 and/or benefit from coupling with the power supply line.

Naturally, the element 41 can also be a transceiver for sending commandacknowledgement or successful command execution signals or evenoperating fault signals.

The control board 4 also contains a processing logic unit 42, forexample a microcontroller, so as to control the electrical power supplyof the motor on the basis of the commands received. A motor currentsensor, not represented, is used for example to analyze the motortorque. It can be linked to a speed or position sensor linked to themotor and/or to the output shaft of a reduction gear 6. These elementsare known to those skilled in the art.

Advantageously, the control board 4 and the converter 3 are mounted onone and the same printed circuit. The power that supplies the controlboard is normally drawn from the output voltage of the converter 3, butit may also be advantageous to use a separate power supply circuit, atleast to supply the radio-wave receiver when the latter is in the“standby” state.

The DC motor 5 is powered from the converter 3 under the control of theboard 4. It is the consumption of the latter that mainly set the size ofthe converter. The reduction gear that follows it in the kinematic chaingenerally comprises at least two reduction stages.

The above assembly of elements is mechanically inserted into a tubularor parallelepipedal enclosure 7 made of steel, plastic material orcomposite material. The openings required for entry of the electricalpower supply cable and the output shaft are provided with sealing meansfor preventing dust and splashed water from entering into the enclosure.

This assembly 10 is itself inserted into an element longer than thewinding tube of a blind or a shutter, or even the casing of a venetianblind. This element is normally made of steel.

For the powers concerned (measured in tens of watts) the required spaceis approximately 20 or so cubic centimeters in cylindrical form,typically having a diameter of between 20 and 40 mm. In theseconditions, a power supply unit comprising only passive orunidirectional elements causes unacceptable overheating, unless theoperation times are considerably limited. It will therefore beadvantageously replaced by a switched power supply unit 3, whichincludes at least one switch 3 a, controlled at a frequency F1. A smalltransformer can be added to the converter assembly.

In other fields, and also in the field of actuators for solar protectionmeans, such power supplies are known to those skilled in the art, withdifferent topologies. For example, the applicant markets a switched-modepower supply unit for powering, from the mains supply, a plurality oftubular actuators operating at a DC voltage of 24 volts.

It is in particular known that the higher the frequency F1, the smallerthe volume of the power supply for a given power. Frequencies of 80 kHz,even higher than 100 kHz, are, consequently, commonly used.

The harmonics induced by the switching of the switch 3 a(or theswitches) are incompatible with the presence of a radio-wave receiver 41within the actuator and this effect increases with the ratio F1/F0.

Being enclosed in a tube or metal casing serving as a screen and notbeing linked to an external, large-sized antenna, the receiver used musthave a very high sensitivity. It is therefore very vulnerable toradiated interference.

When confronted with a problem of cohabitation between afrequency-controlled switched power supply and between a radio-wavereceiver, it is resolved either by component shielding and spacingtechniques, or by filtering techniques, or by use of a particular typeof switching mode enabling the power supply to operate in resonant orquasi-resonant mode. More often than not, a combination of these methodsis used. Patents U.S. Pat. No. 5,642,274, U.S. Pat. No. 5,528,481 andU.S. Pat. No. 4,688,614 disclose examples of these techniques. It shouldbe noted that, in the case of a television for example, there issufficient space to separate the critical assemblies and so minimizecoupling effects.

Without using additional and costly shielding and filtering elements, itwould seem out of the question in principle for a person skilled in theart to position in the immediate vicinity, and even more so on one andthe same printed circuit board, a frequency-controlled switched powersupply and a high sensitivity radio-wave receiver.

The invention does, however show that this is possible at aneconomically sustainable cost and even doing without a power supplyoperating in resonant mode. This possibility relies on compliance withparticular frequency conditions.

FIG. 2 diagrammatically represents an asymptotic diagram of the costs,in logarithmic scale, versus the ratio of the frequencies F1/F0, for agiven motor power. The costs are expressed in octaves (doubling for eachinterval) and the ratios of the frequencies in decades.

The curve 22 represents the overall functional costs, in other words,the costs needed to produce the converter 3 and the control board 4provided with the receiver 41 in a given space. In this example, thespace cross section is fixed and the length is free.

Given the regulations, the frequency of the radio-waves in this type ofapplication can be situated at approximately 100 kHz, and/or on thefrequencies used for RFID-type proximity communications or can even begreater than a megahertz (for example, 27, 433, 868 or 2400 MHz).Without the benefit of the mass production effects associated withparticular applications, the costs needed to produce the radio-wavereceiver are relatively unaffected by the frequency. For example, AMdetection of 100 kHz-type frequencies is easier than FM detection at 433MHz. The larger dimension of the components in the first case is offsetby their smaller number.

In a first approximation, the cost of the overall functional componentstherefore depends far more on the frequency F1 of the converter than onthe frequency F0 of the receiver.

In practice, except in the particular case where the switching frequencyF1 of the power supply unit is equal to the mains supply frequency ortwice the latter, increasing the frequency F1 means that the transformerof the power supply unit and the storage capacitor limiting ripple onthe output voltage can be miniaturized. This miniaturization is indeedreflected in the use of slightly more expensive components (ferrite coreof transformers, switching transistor used as switch), but this cost ismore than offset by the reduction in the space volume and theimprovement in thermal performance which are directly linked toefficiency. The overall functional cost (represented by the curve 22)therefore decreases when the frequency F1 increases and therefore whenthe ratio F1/F0 increases.

Conversely, the use of a switched power supply unit controlled at thefrequency of the mains supply or at a low frequency that is a multipleof the mains supply frequency is reflected in a significant drop in thecost of production of the converter and therefore the overall functionalcost, since it allows the use of a transformer with a core consisting ofconventional plates and not of ferrite. Such a power supply is describedfor example in patent U.S. Pat. No. 5,818,708. This fall in cost isparticularly great given that, for low frequencies, a ferrite coretransformer presents large dimensions.

The filtering cost is represented by the curve 21. Filtering isunderstood here to mean any shielding or attenuation element enablingthe assembly to remain functional, once the elements are positioned inthe immediate vicinity of each other in the enclosure 7, and enablingthe standards to be observed. The filtering required by the motor isalso taken into account. Filtering is applied to the radiated andconducted interference modes.

Apart from the low switching frequency values of the power supply F1,this curve increases with the ratio of the frequencies F1/F0: the higherthis ratio, the more the converter affects the receiver. The more theratio increases, the more this filtering cost is due to the cohabitationof the elements.

For low values of F1, in particular equal to or multiples of the mainssupply frequency, the converter operates in a mode that strongly affectsconducted mode interference. The result is an additional filtering cost,dictated by regulatory requirements.

The overall cost is represented by the curve 23, sum of the functionalcosts and the filtering costs.

It will be noted that there are two areas of minimum overall cost: oneZ1 corresponding to a very low value of the ratio F1/F2, the other Z2situated either side of a value approximately equal to 7 10⁻⁵.

The area Z1 corresponds to the particular case already mentioned of aswitch control frequency equal to or double that of the AC power supplynetwork.

In the second area Z2, every effort is therefore made to satisfy theoptimum condition on the ratio F1/F0. As an example, a control frequencyequal to 30 kHz corresponds to the optimum for a frequency of 429 MHz.

It is, however, clear that this optimum allows a slight increase incost, to favor a smaller space. An appropriate extent corresponds to adecade centered on this value.

The chosen ratio can therefore vary within a range between 7/√10 10⁻⁵(approximately 2.2 10⁻⁵) and 7/√10 10⁻⁵ (approximately 2.2 10⁻⁴), whilecomplying with the teaching of the invention relative to the area Z2. Toexpress this the other way round, the limits of this ratio consist onthe one hand in situating the frequency F0 as being at least greaterthan 4500 times the frequency F1; and, on the other hand, in taking avalue F0 less than 45000 times the frequency F1.

If the teachings of the invention are observed, it is consequently notincompatible to use a converter with frequency controlled switch and aradio-wave receiver within a confined space involving strong interactionof the elements, nor even to locate these functions on one and the sameprinted circuit board.

Furthermore, the invention then allows, at lower cost, for the use of areceiver offering high sensitivity, and the antenna of which is disposedinside the enclosure of the actuator.

Specific embodiments of an electrical actuator having a direct currentmotor according to the present invention have been described for thepurpose of illustrating the manner in which the invention may be madeand used. It should be understood that implementation of othervariations and modifications of the invention and its various aspectswill be apparent to those skilled in the art, and that the invention isnot limited by the specific embodiments described. It is thereforecontemplated to cover by the present invention any and allmodifications, variations, or equivalents that fall within the truespirit and scope of the basic underlying principles disclosed andclaimed herein.

1. An electrical actuator configured to operate a closing, darkening orsolar protection element and operatively coupled to a mains inputvoltage source having a mains frequency, the actuator in a commonenclosure comprising: a direct current motor; a control board configuredto control the motor; an AC/DC voltage converter configured to convertand lower the input voltage source and having at least one switchoperating at a switching frequency (F1); a radio frequency (RF) receiverconfigured to receive external signals at a receiver frequency (F0); andwherein the switching frequency is less than twice the mains frequencyand/or the ratio of the switching frequency (F1) to the receiverfrequency (F0) ranges between 2.2×10^−5 and 2.2×10^−4 so that energygenerated by the AC/DC voltage converter does not interfere with the RFreceiver.
 2. The electrical actuator as claimed in claim 1, wherein theAC/DC voltage converter comprises a voltage transformer.
 3. Theelectrical actuator as claimed in claim 1, wherein the AC/DC voltageconverter and the control board are mounted on the same printed circuit.4. The electrical actuator as claimed in claim 1, wherein the radio-wavereceiver of the control board is provided with an antenna located insidethe enclosure of the actuator.
 5. The electrical actuator as claimed inclaim 2, wherein the AC/DC voltage converter and the control board aremounted on the same printed circuit.
 6. The electrical actuator asclaimed in claim 2, wherein the radio-wave receiver of the control boardis provided with an antenna located inside the enclosure of theactuator.
 7. The electrical actuator as claimed in claim 3, wherein theradio-wave receiver of the control board is provided with an antennalocated inside the enclosure of the actuator.
 8. The electrical actuatoras claimed in claim 5, wherein the radio-wave receiver of the controlboard is provided with an antenna located inside the enclosure of theactuator.